Mobile antennas built for mounting on trucks, tanks, etc. must be designed and installed to pass under bridges etc. having less than approximately 14 feet road clearance. A problem has occurred when these antennas strike a bridge etc. when the antenna is moving at a high rate of speed. Antennas for the 27 mHZ band for example produce a wave length of about 32 feet. A half wave length is impractical for a vertical whip, and a quarter wave length must have an electrical length of about 96 inches. Quarter wave length antennas must be attached above a metal structure in which a mirror image quarter wave is produced, so for many applications, even the quarter wave length antenna must be physically shortened for mobile use by using a loading inductance to give the antenna a proper impedance to match the driving equipment. It is desired therefore to produce a rugged antenna whose point of attachment has an impedance of approximately 50 ohms. All prior art base loaded antennas of which I am familar only have an impedance of approximately 30 ohms.
The prior art with which I am familar produces a quarter wave length antenna having 50 ohms impedance by separating a top whip of approximately 24 inches, from a lower whip of approximately 18 inches by a 6 inch plastic connector surrounded by an inductance. The inductance gives the two sections of whip the necessary electrical length, and the impedance coil must be inserted in the center section of the antenna in order to give its lower end attachment the desired 50 ohms.
An object of the present invention therefore is the provision of a new and improved base loaded whip antenna having approximately 50 ohms impedance, and which is rugged in construction, efficient in its operation, and inexpensive to manufacture.
Further objects and advantages will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiment described with reference to the accompanying drawings forming a part of this specification.